Psilotaceae

Psilotaceae is a small family of fern-like plants within the division Pteridophyta. It comprises two genera, Psilotum and Tmesipteris, with a modest number of species. Members are commonly known as whisk ferns and are among the most primitive living vascular plants.

Morphology and ecology: The sporophyte consists of simple, green stems that branch dichotomously. The plants lack true leaves and roots; leaf-like structures are reduced to minute enations along the stems. They have underground rhizomes and rely partly on fungal associations for nutrients. The stems are often photosynthetic and can be terrestrial, epiphytic, or xeric-adapted in humid habitats.

Reproduction: Sporangia are produced in synangia, fused clusters borne on short stalks along the stems. The spores are homosporous, germinating to yield a small, usually subterranean gametophyte that commonly relies on mycorrhizal fungi for nourishment.

Distribution and habitat: Psilotum nudum has a near-circumtropical distribution, while Tmesipteris occurs in eastern Australia, New Zealand, and some Pacific islands. They are typically found in moist forest environments, on decaying wood, or as epiphytes, and favor humid, shaded conditions.

Taxonomy and evolutionary significance: Psilotaceae is placed in the order Psilotales. They are regarded as a primitive lineage of ferns, retaining features such as dichotomous branching and the absence of true roots and leaves. Molecular data support Psilotum and Tmesipteris as a distinct, closely related group within the ferns, offering insights into early vascular plant evolution.